I noticed that our WiccaPlus app has Imbolc as today, but my witchy calendar has it as Tuesday. Interesting.

I suppose there can be some variations on the exact day.

Most people celebrate Imbolc on Feb 1st.
But some traditions celebrate in on the day that is halfway between the Winter Solstice and the Spring Equinox when the Sun is at 15° in Aquarius. This date varies from year to year, but usually falls around Feb 5th.